After putting up with inferior quality trimmers on a Cubic Astro 103 for too long, I would like to replace them with what I know to be high quality trimmers. Single-turn cermet trimmers from Beckman Industries are high quality, dependable, reliable trimmers. But, I have been unable to find a source in any web searches.

With no results following ebay offerings and on-line suppliers for several months, I contacted Beckman, and discovered that all the Helitrim products are now RoHS compliant (lead free). And, adding the RoHS compliant "LF" suffix to the BI part numbers in supplier's search engines, yielded positive "availabilty" results. That's not to say "in-stock", as the so-called just-in-time philosophy dictates that supplier inventories are....for all practical purposes....non-existent. I've ordered the parts from one of the major parts suppliers, andf they're all on back-order, with no projected or estimated ship-dates as yet.

I sure miss having local brick-and-mortar supply houses, that actually have parts in stock. The LAST remaining supply house here in the Phoenix area that had on-hand stock for radio entusiasts (Capital Electronics), closed their doors last year. The only remaining supply houses with on-hand stock are now for industrial electronics/electrical and computers.

The "just-in-time" philosophy may support development and production programs, where needs can be anticipated or planned. But......it sure doesn't do much to satisfy repair demands.....which are seldom anticipated or planned.

Why is it important that you use single turn trimmers? I long ago switched to 10 turn trimmers for most applications in my radio and audio gear. Compared to single turn trimmers, they're just about immune to value changes caused by vibration. Bournes is a good brand, but I've very good success with the Chinese copies available on eBay. They're available in a variety of control and lead configurations so just about any of the single turn trimmers can be replaced by a 10 turn trimmer.

Why is it important that you use single turn trimmers? I long ago switched to 10 turn trimmers for most applications in my radio and audio gear. Compared to single turn trimmers, they're just about immune to value changes caused by vibration. Bournes is a good brand, but I've very good success with the Chinese copies available on eBay. They're available in a variety of control and lead configurations so just about any of the single turn trimmers can be replaced by a 10 turn trimmer.

I have replaced some single-turn trimmers with multi-turn where applicable/compatible. However, there are mechanical, electrical, and even procedural (adjustment) demands that can, and do, preclude use of multi-turn trimmers to replace single-turn trimmers:

Mechanical: Mounting footprint of multi-turns are larger than single-turns. Densely populated boards cannot always accommodate larger device footprints. Single-turns which are board-mounted with adjustment access via cabinet access holes, provide wiper adjustment access centered on the trimmer mounting pattern. Cabinet covers shouldn't have to be removed to accomplish modification or adjustment of operating features intended to be adjustable without disassembly.

Electrical: Generally, multiturn cermet trimmers have about 1/2 the power dissipation capability of similar size (actually smaller footprint) single-turn trimmers. Enclosed resistive substrates cannot dissipate power as well as open-frame/exposed resistive substrates.

Procedural: Some trimmer adjustment procedures fall into the "time is of the essence" demand, where adjustments must be accomplished in a minimum (and sometimes specified) amount of time. Such is the case with adjustment of PA monitoring and control circuits which must be performed with a "key down" condition. In general, the adjustment of a multi-turn trimmer will consume more time in a key-down condition, than will adjustment of a single-turn trimmer. Excessive time spent in key-down conditions of a PA that has not yet been adjusted for spec operation, can yield very unsat results.

Just one additional note. The Beckman Helitrim model 91 series trimmers are (in my 50+ years of experience) far superior in quality, reliability, and expected operational life than any other single-turn trimmer out there. I've never had one go intermittent, or lose wiper contact tension, or develop "cold" spots on the element.

As a rule, engineers of quality equipment design for quality to be delivered. However, sometimes (more often now, than ever) bean counters insert their will at the conclusion of a successful design/development effort of a quality product, and reduce cost by replacing quality devices with lowest-bid inferior devices. This, I have to believe, is the case with the Cubic 103 trimmers. Too often, those "directed" cost reduction initiatives result in little actual cost reduction or profitability, and more often result in loss of a "quality" reputation, and subsequently the loss business or market share.

Good points, but in all the instances I've run into, I've been able to work around them. I haven't yet run into a situation where the multi-turn wouldn't fit in the available space, but I can see where that could be a problem in very high density SMD boards. Some of the little pots are hard to see, let alone adjust. Other than the high density stuff, I've always been able to find a variation of package that allowed me to maintain the existing adjustment holes without problem. Regarding the "time is of the essence" situation: agreed that can be a real problem. I usually measure the tap position of the trimmer I'm removing and then set the multi-turn replacement to nearly the same value. So, the time to final adjustment probably isn't any longer than struggling to find the sweet spot on the single turn trimmer.

Maybe the quality trimmers you mentioned don't exhibit the difficulty of setting to a precise position? That's been my number one gripe with the trimmers I usually run into.

Good points, but in all the instances I've run into, I've been able to work around them. I haven't yet run into a situation where the multi-turn wouldn't fit in the available space, but I can see where that could be a problem in very high density SMD boards. Some of the little pots are hard to see, let alone adjust. Other than the high density stuff, I've always been able to find a variation of package that allowed me to maintain the existing adjustment holes without problem. Regarding the "time is of the essence" situation: agreed that can be a real problem. I usually measure the tap position of the trimmer I'm removing and then set the multi-turn replacement to nearly the same value. So, the time to final adjustment probably isn't any longer than struggling to find the sweet spot on the single turn trimmer.

Maybe the quality trimmers you mentioned don't exhibit the difficulty of setting to a precise position? That's been my number one gripe with the trimmers I usually run into.

Yes, when replacing a trimmer in a circuit where the initial value is critical, I try to pre-set the replacement value to minimize circuit trauma. And, yes, the Helitrims don't exhibit the all too typical "jumping", "skipping", or hysteresis that's so aggravating (and, in the case of PA's, potentially costly)....only smooth, seamless wiper output without any discontinuities. The Helitrims scream "quality", and "close-tolerance" that are missing in the other famous-label trimmers. No radial or axial slop of the wiper rotor, and no perceptible slop or wobble between the wiper and element pieces. They are really tightly coupled, and I've never had any changes in setting caused by vibration, shock, or temp cycling. I only hope that the new crop (RoHS compliant) production are the same high quality as those in my old-production spares trays. Here's hoping.....

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